Conventional wall box cover plates, referred to herein as face plates, are usually in the form of a flat plate having one or more openings providing access to a wiring device within a wall box. The purpose of the face plate is to provide a decorative cover for the wall box installation while preventing operator exposure to the interior of the wall box which contains electrical wiring. As used herein, "wiring device" refers generally to electrical power control/distribution devices, including but not limited to ON/OFF switches, membrane switches, touch pad switches, light dimmer controls, motor speed controls, power outlets and the like, and to certain communications/data connectors such as telephone jacks, coaxial cable connectors, TV antenna connectors, and computer network cable connectors.
Wiring devices conforming to NEMA standards include a metal yoke or mounting strap with oversized mounting holes which permit horizontal position adjustment of the wiring device within a wall box. The yoke strap also includes one or more threaded mounting holes for attaching the face plate by screw fasteners to the yoke strap, thereby completing the enclosure of the device and wiring terminations within the wall box.
The enclosed wiring device may have an externally projecting switch actuator, control knob, toggle arm, power receptacle or the like which is supported on the mounting strap by an insulating escutcheon. The face plate access opening is closely conformed about the escutcheon to expose the projecting device portion while limiting operator access to electrical terminals and wiring within the wall box. Some wiring devices, for example membrane switches and touch pad switches, have pressure responsive actuator surfaces which are flush mounted within the access opening.